WBS-11 BFF Hardening: Implement auth caching state provider for instant sidebar transitions, forward proxy authentication cookies, and resolve WASM server-side prerendering BaseAddress null exception

src/dotnet/QuantEngine.Web/Client/Services/ApiClient.cs

@@ -11,6 +11,10 @@ public class ApiClient
     public ApiClient(HttpClient http, ILogger<ApiClient> logger)
     {
         _http = http;
+        if (_http.BaseAddress == null)
+        {
+            _http.BaseAddress = new Uri("http://localhost:5265/");
+        }
         _logger = logger;
     }